Windsor Group Research Articles

Evaluation of CO2 storage potential of Carboniferous sandstones in the Maritime Provinces of Canada

The suitability of Carboniferous sandstones in three regions of the Maritime Provinces of Canada for geological carbon storage was evaluated: the Horton Bluff Formation in the Windsor Sub-basin, the lower Cumberland Group sandstones in the Cumberland–Sackville Sub-basin, and the Pennsylvanian sandstones of Prince Edward Island. the properties of potential reservoirs and characteristics of vertical seals and barriers to lateral migration were evaluated using previously collected well logs, sample descriptions, core analyzes and seismic interpretations. Reservoir quality was found to be the limiting factor in all three regions. Sandstones in the upper Hurd Creek Member of the Horton Bluff Formation locally have porosities up to 15% and permeabilities up to 25 milliDarcies at depths up to 1200 m. their aggregate thickness may be suitable for GCS, but individual sandstones are thin and likely of limited lateral extent. the lower Cumberland Group contains sand-dominated successions up to 1 km thick with low porosity (5–7%) where known in the subsurface. Sandstone bodies in the Bradelle, Green Gables, and Cable Head formations beneath Prince Edward Island exceed tens of meters in thickness with porosities averaging up to 10–12% and permeabilities up to 10 milliDarcies. Evaporites in the overlying Windsor Group would provide a suitable seal for the Horton Bluff Formation; in other areas the top seal would be provided by mud-prone heterolithic intervals. the evaluated areas may provide opportunities for small onshore storage projects. Further work is warranted to delineate reservoir trends and verify the integrity of potential top seals and traps.

A fresh look at the Gulf of St. Lawrence, Eastern Canada: Geophysical imaging of salt bodies and volcanic rocks in the upper Paleozoic Magdalen Basin

In the Gulf of St. Lawrence, the late Middle Devonian to early Permian Magdalen Basin hosts numerous salt bodies, but their number and geometry remained poorly constrained due to the poor quality of industry-seismic data. Salt originates from the Middle Mississippian (Visean) Windsor Group, which includes marine carbonates and evaporites. In this study, we use multibeam bathymetry as well as unpublished aerogravity and aeromagnetic data to better characterize the geometry of salt bodies. These datasets show a high degree of coherency and illustrate deformation on the seafloor, gravity lows and magnetic highs, all associated with salt bodies and overlying volcanic rocks. In map view, the geometry of individual salt bodies varies from nearly circular to ovoid and strongly elongated. Some salt bodies coalesce in complex-shaped salt walls elongated NNE, parallel to some of the faults that controlled the early stages of the Magdalen Basin development. Forward modeling indicates that low density salt bodies overlain by a 100–300 m thick volcanic pile may account for both gravity and magnetic signals. The ubiquity of mafic volcanic rocks indicates that the late Visean to Serpukhovian volcanic episode is more voluminous than previously thought. This episode is possibly associated with a series of dykes continuous for up to 225 km and with a period of underplating now recorded by a lower crustal layer with high seismic velocity.

A primary evaporite weld revealed in the late Paleozoic Antigonish sub-basin of Nova Scotia

The Antigonish sub-basin lies within the late Paleozoic Maritimes Basin of Atlantic Canada. Late Devonian to early Carboniferous basin development resulted in a basin-and-range topography, within which the clastic Horton Group was deposited in grabens and half-grabens. The overlying Viséan Windsor Group contains substantial evaporite units; later basin development was accompanied by expulsion of these evaporites. In the Antigonish sub-basin, a significant stratigraphic omission surface initially described as a thrust was subsequently reinterpreted as the extensional Ainslie Detachment. This surface can be examined in drill-core, where the halite-bearing interval is reduced to 3.8 m of halite-cemented breccia of sedimentary rock fragments. The halite cement is sub-horizontally foliated and lineated. At Lakevale, an outcrop section of the Windsor Group is reduced in thickness to tens of metres. Above a basal limestone unit containing pseudomorphs of gypsum, most of the Windsor Group is represented by sedimentary-clast breccias that resemble those seen in core, but with the halite removed by solution in the near-surface environment. The stratigraphic record within the sub-basin implies that expulsion of lower Windsor salt was initially toward the edges of the basin where rising diapirs blocked the deposition of middle Windsor group, but in the basin centre a second salt unit was deposited. Subsequently, during contractional inversion of basin-bounding faults, the middle Windsor salt was expelled into diapirs near the centre of the basin. The Ainslie Detachment is reinterpreted as a primary salt weld: a boundary between units formerly above and below expelled lower Windsor evaporites. The resulting stratigraphic omissions and structures match those seen above expelled evaporite layers on continental margins.

Petrographic Record and Conditions of Expansive Hydration of Anhydrite in the Recent Weathering Zone at the Abandoned Dingwall Gypsum Quarry, Nova Scotia, Canada

In the Dingwall gypsum quarry in Nova Scotia, Canada, operating in 1933–1955, the bedrock anhydrite deposits of the Carboniferous Windsor Group have been uncovered from beneath the secondary gypsum beds of the extracted raw material. The anhydrite has been subjected to weathering undergoing hydration (gypsification), transforming into secondary gypsum due to contact with water of meteoric derivation. The ongoing gypsification is associated with a volume increase and deformation of the quarry bottom. The surface layer of the rocks is locally split from the substrate and raised, forming spectacular hydration relief. It shows numerous domes, ridges and tepee structures with empty internal chambers, some of which represent unique hydration caves (swelling caves, Quellungshöhlen). The petrographic structure of the weathering zone has been revealed by macro- and microscopic observations. It was recognized that gypsification commonly starts from a developing network of tiny fractures penetrating massive anhydrite. The gypsification advances from the fractures towards the interior of the anhydrite rocks, which are subdivided into blocks or nodules similar to corestones. Characteristic zones can be recognized at the contact of the anhydrite and the secondary gypsum: (1) massive and/or microporous anhydrite, (2) anhydrite penetrated by tiny gypsum veinlets separating the disturbed crystals and their fragments (commonly along cleavage planes), (3) gypsum with scattered anhydrite relics, and (4) secondary gypsum. The secondary gypsum crystals grow both by replacement and displacement, and also as cement. Displacive growth, evidenced by abundant deformation of the fragmented anhydrite crystals, is the direct cause of the volume increase. Crystallization pressure exerted by gypsum growth is thought to be the main factor generating volume increase and, consequently, also the formation of new fractures allowing water access to “fresh” massive anhydrite and thus accelerating its further hydration. The expansive hydration is taking place within temperature range from 0 to ~30 °C in which the solubility of gypsum is lower than that of anhydrite. In such conditions, dissolving anhydrite yields a solution supersaturated with gypsum and the dissolution of anhydrite is simultaneous with in situ replacive gypsum crystallization. Accompanying displacive growth leads to volume increase in the poorly confined environment of the weathering zone that is susceptible to upward expansion.

New insight on the geometry and evolution of the Moncton sub-basin from 3D seismic reflection data in the McCully area, New Brunswick, Canada

Abstract Within the Maritimes Basin of eastern Canada, the onshore Moncton sub-basin is one of the NE-trending second-order depocenters that recorded a complex tectonic history from Late Devonian to Late Carboniferous. Analysis of a 3D seismic volume in the McCully gas field area exemplifies the complex interplay between mainly continental sedimentation and several tectonic episodes that contribute to a net extension or shortening in an overall strike-slip setting. The new interpretation demonstrates the role of normal faults oblique to the sub-basin axis in initial phases of sub-basin development and their influence on the deposition of the Upper Devonian-Lower Mississipian Horton Group sediments. A subsequent episode of transpression is recorded by syn-folding growth strata (base of the Mississipian Sussex Group) preserved on both flanks of an anticline that belongs to a fold system that shows an en echelon geometry relative to sub-basin bounding faults. Deposition of a marine interval (Middle Mississipian Windsor Group), including evaporitic strata is succeeded by an halokinetic growth succession (Upper Mississipian-Pennsylvanian Mabou Group) found in minibasins that formed through drape folding (downbuilding) in response to salt-walls development. This polyphased history illustrates the complexity of strike-slip basins that are often controlled by structures with different geometry and kinematics in time and/or space.

Sedimentology and chemostratigraphy of Carboniferous red beds in the western Moncton Basin, Sussex area, New Brunswick, Canada: possible evidence for a middle Mabou Group unconformity

The area around Penobsquis, east of Sussex, New Brunswick, Canada, is an important location of natural resources for the province. The McCully gas field produces from strata of the Mississippian Horton Group whereas younger strata of the Windsor Group are host to major potash and rocksalt deposits. Overlying these units are over 1 km of poorly understood red beds currently assigned to the Mississippian Mabou Group. To date, this latter unit lacks significant marker beds and has had no useful biostratigraphic recovery, despite recent extraction of close to 5 km of drill core. Research on this core broadly identifies siltstone and sandstone at the base of the Mabou Group that gradually coarsen up into conglomerate. The succession is considered the result of alluvial-fan progradation from the northeast. Within this succession, in several of the cores, is a single interval of localized, horizontally laminated to cross-stratified, bluish-grey sandstone, containing carbonaceous plant fragments and siltstone intraclasts. To assess the importance of this interval in the context of the red bed succession, a total of 131 samples of core from three boreholes have been analyzed using Inductively Coupled Plasma and spectroscopic techniques to determine chemostratigraphy. Study of various elemental ratios can delineate two packages, one that corresponds to the grey interval and overlying red beds, and the other to the underlying red beds. Changes in the elemental ratios are interpreted to mark a broader population of mineral species related to greater variation of provenance and diagenesis in the upper sediment package. The reduced horizons and rip-up clasts may have been produced by sediment reworking along a boundary that represents an unconformity (in core, a disconformity) at a stratigraphic level near to where one has been inferred by other workers.

Introducing Digital Media to Automotive Industry: The Role of Corporate Blogging and Economic Context in Full-Funnel Digital Marketing

Introducing Digital Media to Automotive Industry: The Role of Corporate Blogging and Economic Context in Full-Funnel Digital Marketing

Deposition of a saline giant in the Mississippian Windsor Group, Nova Scotia, and the nascent Late Paleozoic Ice Age

Saline giants are vast marine evaporite deposits that currently have no modern analogues and remain one of the most enigmatic of chemical sedimentary rocks. The Mississippian Windsor Group (ca. 345Ma), Maritimes Basin, Atlantic Canada is a saline giant that consists of two evaporite-rich sedimentary sequences that are subdivided into five subzones. Sequence 1 is composed almost entirely of thick halite belonging to Subzone A (Osagean). Sequence 2 is in unconformable contact and comprised of stacked carbonate-evaporite peritidal cycles of Subzones B through E (Meramecian). Subzone B, the focus of research herein, documents the transition from wholly evaporitic to open marine conditions and thus, preserves an exceptional window into the processes forming saline giants.Lithofacies stacking patterns in Subzone B reveal that higher-order fluctuations in relative sea level produced nine stacked parasequences interpreted to reflect high frequency glacioeustatic oscillations during the onset of the Late Paleozoic Ice Age. Each parasequence reflects progradation of intertidal and sabkha sediments over subtidal carbonate and evaporite deposits. Dissimilarities in cycle composition between sub-basins imply the development of contrasting brine chemistries from differing recharge rates with the open ocean.What the Windsor Group shows is that evaporite type is ostensibly linked to the amplitude and frequency of sea level rise and fall during deposition. True saline giants, like the basinwide evaporites of Sequence 1, apparently require low amplitude, long frequency changes in sea level to promote the development of stable brine pools that are only periodically recharged with seawater. By contrast, the high amplitude, short frequency glacioeustatic variability in sea level that controlled the accumulation of peritidal evaporites in Subzone B produce smaller, subeconomic deposits with more complex facies relationships.

Basement-cover relations in the southeastern Cape Breton Highlands, Nova Scotia, Canada

In the southeastern Cape Breton Highlands Neoproterozoic plutonic and metamorphic rocks outcrop in upland areas whereas Carboniferous sedimentary rocks are found in the river valleys and coastal lowlands. Detailed analysis of the contacts between these two groups of rocks including mapping, geometric constructions of the contact relations, structural geological investigations, petrographic analysis and geophysical map interpretations show that the basement rocks were emplaced by a thrust fault that extends at least from the Baddeck River valley to North River, and possibly includes klippen south and east of the highlands. The thrust fault transported a slab of rock with minimum thickness of 200 m a distance of at least 8 km over Horton and Windsor group rocks. East-directed translation of the thrust block likely occurred during the Alleghanian orogeny, and appears to mirror movement previously identified in the northern and western Cape Breton Highlands, implying that much of the upland geology is allochthonous, but likely rooted in the central highlands as positive flower structure.

Stratigraphic evolution of provenance in a thick conglomerate-dominated Carboniferous succession in the southern Isle Madame area, Nova Scotia, and paleogeographic implications

Thick conglomerate-dominated sedimentary successions of the Horton and lower Windsor groups in the southern Isle Madame area show provenance variations with stratigraphic position, based on pebble counts, petrographic observations, and facies trends throughout the conglomeratic units. These coarse clastic sediments were deposited in a transtensional basin that formed south of a splay of the Minas Fault Zone, now repeated by younger faults in the study area. A stratigraphic section 1300 m thick that includes the base of the Horton Group was derived mostly, if not entirely, from units in the Avalonian Mira terrane to the east. Similar provenance indications continue stratigraphically upward in this section and elsewhere on Isle Madame through the thick lower and central parts of the Horton Group. In the upper part of the Horton Group, an influx of high-grade metamorphic and deformed plutonic clasts is recorded in the conglomerates, and the percentage of this material continues to increase above a dark fine-grained interval and into the overlying Windsor Group. The metamorphic clasts strongly resemble local basement rocksexposed as belts between conglomeratic domains in Isle Madame, indicating that these deeper crustal rocks were unroofed within the former basin in the late Tournaisian, resulting in redirected drainage patterns. Paleocurrent and facies information suggest that the Mira terrane sources were located to the northwest at the time of deposition. Hence, paleogeographic reconstruction for the area involves not only unroofing of the deeper crustal rocks, but also dextral transcurrent movement to place the appropriate parts of the Mira terrane at the northwestern corner of exposed parts of the basin. This movement was along a subsequently deformed part of the Minas Fault Zone.

Magnetic anomalies associated with salt tectonism, deep structure and regional tectonics in the Maritimes Basin, Atlantic Canada

AbstractThe structure and tectonic evolution of an evaporite basin are investigated in this case study, which combines the interpretation of magnetic data with the more commonly applied seismic reflection and gravity methods. The Maritimes Basin contains up to 18 km of Upper Palaeozoic sedimentary rocks resting on the basement of the Acadian orogeny. Carboniferous rocks are intensely deformed to the southeast of the Magdalen Islands as a result of deformation of evaporites of the Viséan Windsor Group. Short‐wavelength (<5 km) magnetic lineations define NNE‐ and ENE‐trending linear belts, coincident with the mapped pattern of salt structures. Magnetic models show that these lineations can be explained by the infill of subsidence troughs by high‐susceptibility sediment and/or the presence of basaltic rocks, similar to those uplifted and exposed on the Magdalen Islands. Additional shallow, magnetic sources are interpreted to result from alteration mineralization in salt‐impregnated, iron‐rich sedimentary rocks, brecciated during salt mobilization. Magnetic susceptibility measurements of samples from the Pugwash mine confirm the presence of higher susceptibility carnallite‐rich veins within salt units. Salt tectonism and basin development were influenced by the structure of the base group, the deepest regionally continuous seismic reflections (ca. 5–11 km), associated with an unconformity at the base of the Windsor Group, sampled at the Cap Rouge well. Salt structural evolution, formation of the magnetic lineations and geometry of the base group are associated with regional dextral transpression during basin development (late Carboniferous) and/or Alleghanian Orogeny (late Carboniferous to Permian). In this and similar studies, the effective use of magnetics is dependent upon the presence of rocks of high magnetic susceptibility in contrast to the low‐susceptibility salt bodies. In the absence of high‐susceptibility rocks, magnetic lows over the salt structures may be modelled, similar to commonly applied gravity techniques, to derive the internal structure and geometry.

Evaporite tectonics and the late Paleozoic stratigraphic development of the Cumberland basin, Appalachians of Atlantic Canada

Research Article| May 01, 2013 Evaporite tectonics and the late Paleozoic stratigraphic development of the Cumberland basin, Appalachians of Atlantic Canada John W.F. Waldron; John W.F. Waldron † 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada †E-mail: john.waldron@ualberta.ca. Search for other works by this author on: GSW Google Scholar Michael C. Rygel; Michael C. Rygel 2Department of Geology, State University of New York, College at Potsdam, 44 Pierrepont Avenue, Potsdam, New York 13676, USA Search for other works by this author on: GSW Google Scholar Martin R. Gibling; Martin R. Gibling 3Department of Earth Sciences, Dalhousie University, 1459 Oxford Street, P.O. Box 15000, Halifax, Nova Scotia B3H 4R2, Canada Search for other works by this author on: GSW Google Scholar John H. Calder John H. Calder 4Nova Scotia Department of Natural Resources, P.O. Box 698, Halifax, Nova Scotia B3J 2T9, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information John W.F. Waldron † 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada Michael C. Rygel 2Department of Geology, State University of New York, College at Potsdam, 44 Pierrepont Avenue, Potsdam, New York 13676, USA Martin R. Gibling 3Department of Earth Sciences, Dalhousie University, 1459 Oxford Street, P.O. Box 15000, Halifax, Nova Scotia B3H 4R2, Canada John H. Calder 4Nova Scotia Department of Natural Resources, P.O. Box 698, Halifax, Nova Scotia B3J 2T9, Canada †E-mail: john.waldron@ualberta.ca. Publisher: Geological Society of America Received: 28 Apr 2012 Revision Received: 11 Aug 2012 Accepted: 31 Aug 2012 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2013 Geological Society of America GSA Bulletin (2013) 125 (5-6): 945–960. https://doi.org/10.1130/B30718.1 Article history Received: 28 Apr 2012 Revision Received: 11 Aug 2012 Accepted: 31 Aug 2012 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation John W.F. Waldron, Michael C. Rygel, Martin R. Gibling, John H. Calder; Evaporite tectonics and the late Paleozoic stratigraphic development of the Cumberland basin, Appalachians of Atlantic Canada. GSA Bulletin 2013;; 125 (5-6): 945–960. doi: https://doi.org/10.1130/B30718.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Cumberland basin is part of the large and deep Maritimes Basin of Atlantic Canada, interpreted to have developed at tropical latitudes in a tectonic environment of dextral strike slip. The predominantly Mississippian–Pennsylvanian basin fill includes a thick succession of Viséan evaporites of the Windsor Group. An overlying clastic succession includes, in the coal-bearing Cumberland Group, fossil forests with upright trees, preserved at the Joggins Fossil Cliffs United Nations Educational, Scientific, and Cultural Organization (UNESCO) World Heritage Site. Analysis of two-dimensional seismic profiles demonstrates that accommodation for the successions overlying the evaporites was provided by salt expulsion, which led to the development of broad open synclines separated by narrow isoclinal anticlines cored by salt. In the western part of the basin (Athol syncline), evaporites remained largely undisturbed until the Pennsylvanian, when their rapid expulsion accommodated accumulation of the thick Joggins succession. In the eastern part of the basin (Tatamagouche syncline), evaporite withdrawal began in the Viséan and continued during Serpukhovian time, providing accommodation for symmetric and wedge-shaped minibasins filled by Windsor and overlying Mabou Group strata. Only a small volume of evaporites remained to be expelled during Pennsylvanian thrusting along the southern basin margin; as a result, the Cumberland Group is relatively thin. To the north, the Black River, Wallace, and Pugwash synclines developed as minibasins having a character intermediate between the Athol and Tatamagouche synclines. Many of the halokinetic structures in the Cumberland basin are similar to those on salt-bearing passive continental margins. However, the tectonic environment in narrow fault-bounded basins encouraged vertical, rather than horizontal movement of salt and overlying sediments, and has produced characteristic inequant, oval minibasin geometries. These features may be characteristic of salt tectonics in strike-slip basins. Salt expulsion has strongly influenced the distribution of hydrocarbons and other resources in the basin. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Palynostratigraphy of Mississippian and Pennsylvanian rocks, Joggins area, Nova Scotia and New Brunswick, Canada

Carboniferous rocks in the Joggins area, Nova Scotia, and the Maringouin Peninsula, New Brunswick, are world renowned for their well-preserved macroflora, but this paper is the first detailed study of the palynoflora. The section is comprised of the Mississippian Windsor and Mabou groups overlain disconformably by the Lower Pennsylvanian Cumberland Group. The Windsor Group rocks proved to be barren of palynomorphs but the Mabou Group yielded spores and pollen of Brigantian (late Viséan) to Arnsbergian age (early Namurian = early Serpukhovian). The assemblages are assigned successively to the Schopfipollenites acadiensis–Knoxisporites triradiatus, the Grandispora spinosa–Ibrahimispores magnificus, and the Reticulatisporites carnosus Zones. A major palynofloral change takes place between the Mississippian Mabou and the Pennsylvanian Cumberland assemblages. This is believed to reflect a significant regional hiatus in the Joggins section and elsewhere in eastern Canada. The Cumberland Group is characterized by an abundance of Lycospora spp. and monosaccate gymnosperm species of Yeadonian? (Late Namurian = middle Bashkirian?) to late Duckmantian (late Bashkirian?) age. The palynological succession is divided into the Raistrickia saetosa, the Raistrickia fulva, and the Vestispora magna zones. Age determinations of the zones, based on comparisons with Western Europe and the North Sea, are tentative because the Cumberland assemblages lack diversity and many taxa diagnostic in Western Europe are absent in the assemblages of the Joggins area, possibly due to environmental and climatic differences.

Kennetcook thrust system: late Paleozoic transpression near the southern margin of the Maritimes Basin, Nova Scotia

A major zone of deformation affects Early Carboniferous rocks in the southern part of the Maritimes Basin of Nova Scotia, close to the boundary between the Avalon and Meguma terranes of the Appalachians. Field relationships at Cheverie indicate thrusting of Tournaisian Horton Group clastics over Viséan Windsor Group carbonates, evaporites, and clastics, a relationship confirmed by the Cheverie #01 well. Mapped relationships to the south indicate that a system of thrusts, here termed the Kennetcook thrust system, climbs upsection to the southeast, becoming a décollement within Windsor Group evaporites. Industry seismic profiles clearly show deformed Windsor Group, and include fold and fault structures indicative of evaporite flow and solution collapse. Below the Windsor Group, half-grabens filled with Horton Group are clearly imaged; offsets at graben-related faults show that these structures were inverted during later shortening. Above the Windsor Group, less deformed rocks of the Pennsylvanian Scotch Village Formation (Cumberland Group) fill minibasins created by the withdrawal or solution of deformed Windsor evaporites. The timing of thrusting is constrained by these relationships and by crosscutting intrusions to a narrow interval around the Mississippian–Pennsylvanian boundary prior to ∼315 Ma. Deformation was probably related to dextral transpression along the former Avalon–Meguma boundary. Depending on how shortening was transmitted to the southeast, up to 1500 km2 of southern mainland Nova Scotia may be underlain by tectonically transported rocks.

Orbital forcing and Mississippian sea level change: time series analysis of marine flooding events in the Visean Windsor Group of eastern Canada and implications for Gondwana glaciation

Abstract Orbital forcing is strongly expressed in spectra of time series delineating transgressive-regressive (TR) cycles in the late Visean Windsor Group in the Shubenacadie Basin of southern Nova Scotia. These spectra compare closely with those of synthetic, variously degraded time series constructed from summed sine waves representing orbital periods for the eccentricity, obliquity and precession-index as predicted for late Visean time. The introduction of significant new macrofaunal elements in the Windsor Group accompanied transgressions separated in time by 2.2 to 2.4 m.y., perhaps reflecting a longer-period orbital influence by the eccentricity or by modulation of the obliquity. Orbital forcing in the late Asbian substage was apparently dominated by the 100 k.y. eccentricity, whereas in the Brigantian, TR cycles responded mainly to forcing by the 400 k.y. eccentricity. High-magnitude sea-level change in late Visean successions elsewhere, and an orbital signature for Windsor Group TR cycles, suggest that orbitally forced waxing and waning of significant continental ice sheets is the most appropriate explanation for late Visean sea-level change. Ice sheets were fully developed by the end of the early Asbian substage. Sea-level high-stands, interpreted as the result of melting of continental ice sheets, represent a very small temporal percentage of the Windsor Group stratigraphic succession, and mark the late Visean as a cold period in Earth’s history. In this part of Gondwana, a late Asbian or even older start to Gondwana glaciation is indicated, contrasting with the Australian record which places the first significant glaciations of Gondwana in the early Namurian.

Windsor Group (Late Mississippian) stratigraphy, Magdalen Islands, Quebec: a rare eastern Canadian record of late Visean basaltic volcanism

The Magdalen Islands archipelago is the single site in the north-central Gulf of St. Lawrence where surface exposures of the Windsor Group, an important Mississippian (Visean) marine marker interval within the thick Late Devonian-Early Permian fill of the Maritimes Basin, permit stratigraphic comparison with the type Windsor Group and the correlative Codroy Group of western Newfoundland. The presence of volcanic rocks associated with regionally more typical marine carbonate rocks, evaporites, and fine-grained redbeds make this local Windsor Group succession unique in eastern Canada. The volcanic rocks, including vesicular and amygdaloidal basalts with minor pyroclastic rocks, are interstratified in surface exposures with middle Windsor Group gypsum, limestone, and siltstone of late Asbian age. Similar sedimentary suites higher in the Windsor Group, assigned biostratigraphically to the Brigantian and questionably the earliest Pendleian substages, lack any associated volcanic rocks (Île Boudreau) or are in tectonic contact with volcanic-bearing middle Windsor Group successions (Île d’Entreé). The Cap au Diable Formation, erected as a volcanic-dominated rock unit of the upper Windsor Group on the Magdalen Islands, is here abandoned. Thick salt deposits lacking intercalated carbonate rocks, which underlie and are presumed to have diapirically intruded middle and upper Windsor Group strata, are believed to represent the product of the first major cycle of Mississippian marine sedimentation in the region. The Magdalen Islands Windsor Group succession, except for its regionally unique volcanic component, is most comparable to that of south-central and eastern Nova Scotia in its overall character. This tectonically dismembered remnant of an apparently complete succession contrasts with rocks of similar age in southeastern New Brunswick and northwestern Nova Scotia which lack upper Windsor Group marine carbonate members and contain only a limited number of middle Windsor Group marine carbonate bands.
 
 RÉSUMÉ
 
 L’archipel des îles de la Madeleine constitue le seul emplacement dans le Centre-Nord du golfe du Saint-Laurent où des affleurements en surface du groupe de Windsor, intervalle de référence marin déterminant du Mississippien (Viséen) à l’intérieur de l’épaisse couche de remplissage du Dévonien tardif-Permien précoce du bassin des Maritimes, permettent une comparaison stratigraphique avec le groupe type de Windsor et le groupe corrélatif de Codroy de l’Ouest de Terre-Neuve. La présence de roches volcaniques associées à des couches rouges à grains fins, des évaporites et des roches carbonatées marines plus typiques à l’échelle régionale rendent cette succession locale du groupe de Windsor unique dans l’Est du Canada. Les roches volcaniques, notamment des basaltes vésiculaires et amygdaloïdes accompagnés d’une quantité modeste de roches pyroclastiques, sont interstratifiées avec de la siltite, du calcaire et du gypse de la partie médiane du groupe de Windsor dans des affleurements en surface remontant à l’Asbien tardif. Des séquences sédimentaires similaires de niveaux supérieurs du groupe de Windsor, rattachées biostratigraphiquement au Brigantien et de façon discutable aux sous-étages les plus précoces du Pendleien, sont dépourvues de roches volcaniques connexes (île Boudreau) ou se trouvent en contact tectonique avec des successions de roches volcaniques de la section médiane du groupe de Windsor (île d’Entrée). On abandonne dans les présentes la Formation de Cap au Diable, créée à titre d’unité lithologique à prédominance de roches volcaniques de la tranche supérieure du groupe de Windsor dans les îles de la Madeleine. Les dépôts épais de sel dépourvus de roches carbonatées intercalées, sous-jacents, qu’on suppose avoir pénétré diapiriquement les strates médianes et supérieures du groupe de Windsor, représenteraient le produit du premier cycle important de sédimentation marine mississippienne dans la région. La succession du groupe de Windsor et des îles de la Madeleine a, mis à part sa composante volcanique unique à l’échelle régionale, un caractère général très comparable à celle du Centre-Sud et de l’Est de la Nouvelle-Écosse. Ce vestige tectonique-ment démembré d’une succession apparemment complète contraste avec les roches d’âge semblable dans le Sud-Est du Nouveau-Brunswick et le Nord-Ouest de la Nouvelle-Écosse d’où sont absents les membres carbonatés marins de la partie supérieure du groupe de Windsor et qui renferment seulement un nombre limité de bandes carbonatées marines de la partie médiane du groupe de Windsor. [Traduit par la redaction]

SZAIBELYITE: CRYSTAL-STRUCTURE ANALYSIS AND HYDROGEN BONDING

Szaibelyite, ideally MgBO 2 (OH), from the Potash Corporation of Saskatchewan (New Brunswick Division) mine at Penobsquis, Kings County, New Brunswick, occurs in the Upper Halite member of the Windsor Group evaporites, and is associated with halite, sylvite, anhydrite, hilgardite, volkovskite, hydroboracite, walkerite and pringleite. Electron-microprobe analysis, supported by a single-crystal analysis of its structure, yielded: MgO 47.92 (46.28–48.71), FeO 0.74 (0.22–3.05), MnO 0.04 (0.00–0.08), (ideal B 2 O 3 ) 41.77 and (ideal H 2 O) 10.81, for a total of 101.18 wt.%. The empirical formula based on three anions is (Mg 0.99 Fe 0.01 )B 1 H 1 O 3 . Szaibelyite is monoclinic, P 2 1 / a , with refined unit-cell parameters a 12.586(1), b 10.415(1), c 3.1340(3) A, β 95.923(2)°, V 408.6(1) A 3 , Z = 8. The crystal structure refined to an R index of 0.031 using 1,191 unique reflections. The corrugated (100) sheets of [MgO 6 ] octahedra are cross-linked by isolated clusters of [B 2 O 4 (OH)] polyhedra. The [OH] groups strengthen the cross-linkage with hydrogen bonding. The fundamental building block (FBB) within the structure, 2Δ:2Δ, is compared to that in the structures of other borates, such as suanite and clinokurchatovite.

Karst-related outliers of the Cretaceous Chaswood Formation of Maritime Canada

The Lower Cretaceous Chaswood Formation is a terrestrial deposit preserved as scattered outcrops across Maritime Canada. Here we describe newly recognized outliers of the Chaswood Formation near Windsor, Nova Scotia. A Cretaceous age is confirmed only in Bailey Quarry, where sediments are provisionally assigned a Valanginian–Hauterivian (140–130 Ma) age based on palynology, making them among the oldest known deposits of the Chaswood Formation. At three nearby sites, putative Cretaceous sediments are recognized based on similar geological context, facies, and petrography; however, their age cannot be confirmed because sediments either lack palynomorphs or contain equivocal assemblages. Although the Chaswood Formation has been previously documented mainly in small tectonically generated basins, these new-found deposits are fluvial sands and gravels, and lacustrine or floodplain clays associated with a karstified gypsum surface developed on the Carboniferous Windsor Group. Deposits are preserved in karst valleys, sinkholes, and fissures, locally up to 36 m below the paleosurface. Although occupying a karstic setting, sediments were evidently deposited in a through-flowing drainage system because they are quartz-rich and show petrographic similarity to basinal deposits elsewhere. Abundant plant material, including lignite, charcoal, cuticles, and palynomorphs, implies that the surrounding landscape was covered by fire-prone forests of conifers, ginkgos, bennettites, cycads, ferns, and lycopods — typical pre-angiosperm Mesozoic vegetation. Analysis of growth patterns in fossil woods, combined with lithological indicators, suggest a humid, tropical climate, punctuated by aperiodic droughts that may have been accentuated under a karstic hydrological regime.

Transpressional structures on a Late Palaeozoic intracontinental transform fault, Canadian Appalachians

Abstract The east–west Minas fault zone, separating the Early Palaeozoic Meguma and Avalon terranes of the Appalachians, experienced dextral strike-slip motion during the Carboniferous. Abundant oblique contractional structures indicate localized dextral transpression, immediately south of the zone, probably associated with a restraining bend. Subsurface data indicate that the deformed Horton Group clastic rocks are thrust above younger Windsor Group evaporites. Excellent exposures on wave-cut platforms of the Bay of Fundy show structures developed in transpression, including NE-trending upright and inclined folds; south-verging thrust and reverse faults; and NW-striking normal faults. Northwest-trending boudins, which are perpendicular and slightly rotated in a clockwise sense relative to fold hinges, provide a field indicator for dextral transpression. The earliest folds (F 1 ) are curvilinear and may have formed by deformation of wet sediment. F 2 tectonic folds show weak axial-planar cleavage. Locally, these have been rotated into reclined orientations; spectacular downward-facing folds are probably due to refolding by more east–west F 3 folds. The structures observed are consistent with pure-shear-dominated transpression, with the local angle of convergence α increasing over time. This strain history is compatible with progressive strain partitioning, probably associated with the spreading of topography developed at the restraining bend.

Gradual encroachment of a rocky shoreline by an invasive sea during the Mississippian at the southeastern margin of the Maritimes Basin, Nova Scotia, Canada

Onlap of a rocky shoreline by marine beds of the Mississippian Windsor Group occurred at the southeastern margin of the composite upper Paleozoic Maritimes Basin in central Nova Scotia. The sedimentology of thin basal rudaceous deposits suggests that, although the transgression was rapid, there were times of prolonged shoreline stability. Boulder beach deposits indicate a high-energy coastline and a large marine basin. Clastic delta deposits were proximal to thick biohermal banks in shallow areas near the southeast margin of the sea while sulphate deposition was occurring basinward. According to their contained biota and stratigraphic relationships, the marginal banks evolved in a less saline environment than banks forming away from river inputs, on paleotopographic highs located farther offshore. Because diversity of the biota decreases with an increase in both water depth and distance from the paleoshore and because bank development in shallow or marginal areas was apparently synchronous with evaporitic deposition in deeper or less marginal areas, we conclude that both a vertical and a lateral gradient of salinity existed due to the thrusting of fluvial fresh water above salt water and its infiltration along the paleoshoreline. As salinity increased with time, bank building eventually aborted and sulphate deposition gave way to salt deposition in the deepest parts of the basin. Lastly, the onlap of evaporites above marginal clastic deposits indicates that evaporite deposition occurred in a transgressive context, although a gradual thinning of the water column may have simultaneously occurred due to basin infilling.